In the beginning of The Secret Doctrine, Blavatsky establishes three fundamental propositions, which were to become the creed of all later Theosophists:
(a) "An Omnipresent, Eternal, Boundless, and Immutable Principle on which human speculation is impossible".
This of course is the Absolute Reality; the One Reality that is the basis of the Monistic understanding.
(b) "The Eternity of the Universe as a boundless plane", containing periodic "numberless Universes incessantly manifesting and dissapearing".
This is the endless cycles within cycles cosmology of Indian thought. In the Indian religions this is a pessimistic eternity projected into matter, samsara, the cycle of birth and rebirth. But in the more optimistic and evolutionarily orientated cosmology of Blavatsky (and in both of these orientations Blavatsky is "European" or "Western" rather than "Oriental", despite her and her followers' claims to the contrary) it becomes the means by which souls evolve to greater and greater heights.
(c) "The fundamental identity of all souls with the Universal Over-Soul, the latter being itself an aspect of the Unknown Root"
this of course is pure Emanationism -
"and the obligatory pilgramage for every Soul through the Cycle of Incarnation in accordance with Cyclic and Karmic Law"again, the idea of cyclic evolution .
The original Theosophy of Blavatsky, which she herself attributed to a hierarchy of occult "Masters" (I here defer the question of whether the letters attributed to the Masters really were written by Tibetan Adepts, or simply by Blavatsky herself, but it cannot be denied that their style is quite Victorian, and indeed, quite Blavatskyian!) is strongly non-Christian, drawing instead from Indian, Hellenistic, Kabbalistic and contemporary (19th century) Occult and scientific sources. Metaphysically, it is based on concepts such as transcendent monism (the existence of one ultimate principle of being), the hierarchy of secret or occult Masters, cosmic demiurges (the so-called Elohim or dhyan-chohans) rather than a Creator-God, planetary cycles (Rounds and Manvantaras; analogous to the Hindu Yugas and Kalpas), the concept of reincarnation and spiritual evolution towards ultimate divinity and perfection, the still only partially developed idea of seven cosmic planes and seven principles of selfhood (these two not being equivalent, as they were to be in later Theosophy), and an occult theory of human evolution (the so-called Root-Races). The latter also incorporates the idea of previous and now sunken or destroyed continents - Lemuria and Atlantis - where these previous races lived. In short, the whole scheme is dynamic and evolutionary, and still quite fluid.
Later Theosophists - such as C. W. Leadbeater, Rudolph Steiner, and Alice Bailey - retained this basic schema but at the same time Christianised it, usually with Christ or a Christ-like being in a position of great importance in the spiritual hierarchy.